Designing the auditorium’s acoustics
Keiji Oguchi and Marc Quiperez of Nagata Acoustics, personal acoustic consultants to the Ateliers Jean Nouvel, explain their approach to the hall’s acoustics.
What is your role in this project?
Marc Quiquerez: We're helping the Ateliers Jean Nouvel determine the geometry and materials used for the structure and the inside walls of the auditorium.
Keiji Oguchi: In terms of acoustic choices, it's a very different project from the classic "shoe-box" auditorium since the stage is surrounded 360 degrees by the public, in an enveloping form.
What does the fact that the auditorium can accomodate symphony orchestras as well as jazz or world music ensembles imply?
K.O.: The idea is first to create a space dedicated to the "symphonic" use of the auditorium, then to incorporate the adjustments needed for other configurations. For symphonic music, the space needs to be highly reverberative, while for other types of music, like amplified, a long reverberation can create troublesome effects. The sound needs to be absorbed more, temporarily, by using a curtain for example: we're talking about variable acoustics.
What's the difference between echo and reverberation?
M.Q.: They're two completely different things. Reverberation is how long you hear a sound in an auditorium once the music has stopped. The reverberation time can be controlled; the trick is to adjust it. On the contrary, an echo is a problem; the listening experience is disturbed when you hear the same or almost the same sound twice in a row, once coming from the stage and then again from some other direction.
What role does the scale model play in your work?
K.O.: There are three stages. First we locate the echoes, then we determine which surfaces contribute to them. Next, once these problems are solved, we study and confirm the acoustic performance of the auditorium by comparing it to other auditoriums that are known to have excellent acoustics.
How do you reproduce the sounds and listening experience?
K.O.: Since the scale of the model is 1:10, we have to emit sound frequencies ten times higher to reproduce the sound, which can't be heard by the human ear. We use microphones and computers to adjust and pick up the sounds, then we convert them to obtain audible data like in a real auditorium.
Since when have acousticians used models in their work?
K.O.: Since the beginning of acoustics. Before, we used water in two dimensional models to analyse movements on the surface and see how, by comparison, sound waves would spread. Then in 1930, the first tests using 3D models were carried out in Germany.
What are the current requirements or tendencies in acoustics?
M.Q.: The type of sound that's favoured today combines clarity and long reverberation. That being said, although the current quality of recordings has modified our appreciation of sound, most audience members don’t concentrate on these changes. What's more, even if tendencies evolve with innovations made in research labs, the heart of acoustics remains the same. It's the techniques and systems incorporated into the auditoriums that evolve. In other words, there are several objective ways to obtain good acoustics, whereas the results are highly subjective and the modifications, subtle.
K.O.: Conductors and musicians need good sound return. That concerns the acoustics of the stage itself. We’re able to get good results, like here, by installing a wall of sound reflectors – the canopy – about fifteen metres above the stage.
Are there differences in the acoustics between auditoriums in Japan, the US and Europe?
K.O.: Each major auditorium has its own acoustic character, which each audience appreciates differently, and we can't rank them in a certain order. There are cultural differences, but there aren't necessarily major types of auditoriums.
